Pathologic evaluation of thymic hyperplasia in myasthenia gravis and Lambert-Eaton myasthenic syndrome.

Eleven thymectomy specimens from patients with myasthenia gravis or Lambert-Eaton myasthenic syndrome were thoroughly sectioned. The results were compared with the routine surgical pathology reports that were based on a median of four sections. Routine sampling was found to be inadequate because the thymectomy specimens were inhomogeneous--some random sections contained germinal centers while others did not. Thus, on more thorough examination, about half of the specimens should have been diagnosed as showing "follicular hyperplasia" rather than "no diagnostic change" or "involution." This helps explain the conflicting results of previous studies, based when stated on a mean of three sections, in which favorable response to thymectomy in patients with myasthenia gravis was either not correlated with the thymus histologic state or correlated variously with few or numerous germinal centers. Thus, nondiagnostic histologic findings based on only one or two thymus sections should be suspect, and if in doubt a larger number of sections should be examined for accurate pathologic diagnosis.